A study of equivalent source techniques for high-resolution EEG imaging

High-resolution EEG imaging has been an important topic in recent EEG resea rch, and much work has been done on the two equivalent source imaging techn iques: the equivalent distributed dipole-layer source imaging technique (ES T) and the equivalent multipole source imaging technique (SAT), In this pap er we first develop a forward density formula for a spherical equivalent di stributed dipole layer of an arbitrary dipole in a three-concentric-sphere head model. It is clarified using the derived forward formula that the equi valent dipole-layer source and equivalent multipole source are interrelated in theory. Finally, simulation comparisons are conducted, the results of w hich suggest that EST has a higher spatial resolution than SAT when both of them are implemented by a truncated singular value decomposition algorithm . This is due to the different singularities of the inversion equations inv olved in the two techniques. An empirical VEP data study also shows that ES T is better than SAT in providing higher spatial resolution EEG imaging.